package util;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Collection;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * A utility class for parsing and formatting HTTP dates as used in cookies and
 * other headers. This class handles dates as defined by RFC 2616 section 3.3.1
 * as well as some other common non-standard formats.
 * 
 * @author Christopher Brown
 * @author Michael Becke
 */
public final class DateUtil
{
	/**
	 * Date format pattern used to parse HTTP date headers in RFC 1123 format.
	 */
	public static final String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";

	/**
	 * Date format pattern used to parse HTTP date headers in RFC 1036 format.
	 */
	public static final String PATTERN_RFC1036 = "EEEE, dd-MMM-yy HH:mm:ss zzz";

	/**
	 * Date format pattern used to parse HTTP date headers in ANSI C
	 * <code>asctime()</code> format.
	 */
	public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";

	private static final Collection<String> DEFAULT_PATTERNS = 
			Arrays.asList(new String[] { PATTERN_ASCTIME, PATTERN_RFC1036, PATTERN_RFC1123 });

	private static final Date DEFAULT_TWO_DIGIT_YEAR_START;

	static
	{
		Calendar calendar = Calendar.getInstance();
		calendar.set(2000, Calendar.JANUARY, 1, 0, 0);
		DEFAULT_TWO_DIGIT_YEAR_START = calendar.getTime();
	}

	private static final TimeZone GMT = TimeZone.getTimeZone("GMT");

	/**
	 * This class should not be instantiated.
	 */
	private DateUtil()
	{
	}

	/**
	 * Parses a date value. The formats used for parsing the date value are
	 * retrieved from the default http params.
	 * 
	 * @param dateValue
	 *            the date value to parse
	 * @return the parsed date
	 * @throws DateParseException
	 *             if the value could not be parsed using any of the supported
	 *             date formats
	 */
	public static Date parseDate(String dateValue)
	{
		return parseDate(dateValue, null, null);
	}

	/**
	 * Parses the date value using the given date formats.
	 * 
	 * @param dateValue
	 *            the date value to parse
	 * @param dateFormats
	 *            the date formats to use
	 * @return the parsed date
	 * @throws DateParseException
	 *             if none of the dataFormats could parse the dateValue
	 */
	public static Date parseDate(String dateValue,
			Collection<String> dateFormats)
	{
		return parseDate(dateValue, dateFormats, null);
	}

	/**
	 * Parses the date value using the given date formats.
	 * 
	 * @param dateValue
	 *            the date value to parse
	 * @param dateFormats
	 *            the date formats to use
	 * @param startDate
	 *            During parsing, two digit years will be placed in the range
	 *            <code>startDate</code> to <code>startDate + 100 years</code>.
	 *            This value may be <code>null</code>. When <code>null</code> is
	 *            given as a parameter, year <code>2000</code> will be used.
	 * @return the parsed date
	 * @throws DateParseException
	 *             if none of the dataFormats could parse the dateValue
	 */
	public static Date parseDate(String dateValue,
			Collection<String> dateFormats, Date startDate)
	{

		if (dateValue == null)
		{
			throw new IllegalArgumentException("dateValue is null");
		}
		if (dateFormats == null)
		{
			dateFormats = DEFAULT_PATTERNS;
		}
		if (startDate == null)
		{
			startDate = DEFAULT_TWO_DIGIT_YEAR_START;
		}
		// trim single quotes around date if present
		// see issue #5279
		if (dateValue.length() > 1 && dateValue.startsWith("'")
				&& dateValue.endsWith("'"))
		{
			dateValue = dateValue.substring(1, dateValue.length() - 1);
		}

		SimpleDateFormat dateParser = null;
		for (String format : dateFormats)
		{
			if (dateParser == null)
			{
				dateParser = new SimpleDateFormat(format, Locale.US);
				dateParser.setTimeZone(TimeZone.getTimeZone("GMT"));
				dateParser.set2DigitYearStart(startDate);
			}
			else
			{
				dateParser.applyPattern(format);
			}
			try
			{
				return dateParser.parse(dateValue);
			}
			catch (ParseException pe)
			{
				// ignore this exception, we will try the next format
			}
		}

		// we were unable to parse the date
		throw new RuntimeException("Unable to parse the date " + dateValue);
	}

	/**
	 * Formats the given date according to the RFC 1123 pattern.
	 * 
	 * @param date
	 *            The date to format.
	 * @return An RFC 1123 formatted date string.
	 * @see #PATTERN_RFC1123
	 */
	public static String formatDate(Date date)
	{
		return formatDate(date, PATTERN_RFC1123);
	}

	/**
	 * Formats the given date according to the specified pattern. The pattern
	 * must conform to that used by the {@link SimpleDateFormat simple date
	 * format} class.
	 * 
	 * @param date
	 *            The date to format.
	 * @param pattern
	 *            The pattern to use for formatting the date.
	 * @return A formatted date string.
	 * @throws IllegalArgumentException
	 *             If the given date pattern is invalid.
	 * @see SimpleDateFormat
	 */
	public static String formatDate(Date date, String pattern)
	{
		if (date == null)
		{
			throw new IllegalArgumentException("date is null");
		}
		if (pattern == null)
		{
			throw new IllegalArgumentException("pattern is null");
		}

		SimpleDateFormat formatter = new SimpleDateFormat(pattern, Locale.US);
		formatter.setTimeZone(GMT);
		return formatter.format(date);
	}

}